Zoology

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The Anostraca (crustacea : Branchiopoda) of southern Africa.
(1994) Hamer, Michelle Luane.; Appleton, Christopher Charles.
The Anostraca are a group of crustaceans belonging to the class Branchiopoda. They are predominantly restricted to temporary, inland waterbodies, which in southern Africa, include rockpools, animal wallows, and large "pans". The anostracan fauna of southern Africa was last examined in detail in 1929 by Barnard, and recent collecting in a number of areas indicated the need to update earlier work. A total of four genera, each belonging to a separate family, and forty-six species, some of which had not previously been described, are presented in this thesis. The monogeneric family Streptocephalidae is well represented in Africa, and the fauna of Africa south and north of the Zambezi and Kunene Rivers, as well as Madagascar is reviewed. The Streptocephalus species are characterised by having an S-shaped antennal process, terminating in a cheliform "hand" region. The species were divided into ten groups based on similarities in antennal process morphology. The descriptions of five new species have been published, and an update on distribution and specimen data for a number of species are presented. An additional, as yet unpublished new species from Zimbabwe is presented. The genus Artemia, although well researched in other parts of the world, has been largely ignored in southern Africa. Bisexual populations occur along the Cape coast, and a set of specimens from Namibia, which includes only females, may indicate that A. parthenogenetica is also present on the subcontinent. The frontal knob morphology of the Cape specimens is similar to that of A. tunisiana from northern Africa and the Mediterranean. The family Branchipodidae is characterised by the fusion of the basal joints of the male antennae to form a so-called "clypeus". This family is represented in southern Africa by a diverse fauna of the genus Branchipodopsis. Eleven previously described species, as well as five new species are presented. An attempt was made to divide the sixteen species into species groups, as was done for the streptocephalids, but this proved difficult. The taxonomically useful characters in this genus are largely restricted to the basal processes. An additional character, the presence of expansions of the posterior thoracic segments in the females of some species could be useful. Much intraspecific variation in clypeus morphology was evident, particularly in two of the widespread species. Branchipodopsis species commonly occur in small pools which fill a number of times during the wet season and this has probably led to the development of localised adaptations, and intraspecific variation, or even species endemic to very restricted areas. Three sets of specimens which belong to the family Branchipodidae, but to no known genus, were recently collected from north-eastern Natal, the eastern Cape and the Namib desert in Namibia. These specimens share a single, large process positioned medianly on the fused basal joints, as opposed to a pair of processes in this position. However, the morphology of the penes, and the position and form of other antennal processes could indicate that the specimens are not congeneric. Unfortunately, more material is necessary before the descriptions of two of these possible new genera can be published. Three species of the genus Branchinella, of the family Thamnocephalidae, occur in southern Africa. These species have a well developed frontal process, and fully retractible penes. Bran chin ella spinosa was recorded from the Makgadikgadi Pan in northern Botswana, and was probably introduced to this area from north Africa, or Europe, where it has a wide distribution. The other two southern African species have been collected from few localities, and in small numbers, and this may be connected to cyst hatching processes. The southern African anostracan fauna exhibits distinct distribution patterns and these . appear to be influenced by climate, with rainfall having the dominant influence in the western half of the subcontinent, and temperature influencing distribution in the eastern half. The high altitude Escarpment forms a barrier to the movement of species between the coastal margin and the central plateau region. The formation of the Escarpment could have resulted in vicariance speciation in some anostracans, but in most cases, allopatric speciation appears to have occurred. The type of habitat also influences species distribution in a number of ways. The great anostracan species richness in southern Africa is probably related to the climatic heterogeneity of the subcontinent, as well as the possible origin of two genera in Gondwanaland, and the absence of a Pleistocene glaciation in Africa. Large parts of southern Africa have not been sampled, and the exact status and distribution of many species is uncertain.
Aplexa marmorata (Guilding, 1828)(Basommatophora : Physidae) : an invasive freshwater snail in South Africa.
(2000) Dana, Pelisa.; Appleton, Christopher Charles.
Invasions of ecosystems by alien species is a worldwide problem. Man, with his constant travelling, introduces organisms to places they have never occurred in before. The introductions may be accidental or deliberate. Some of the introduced organisms become invasive and some of these also become pests. Two aquatic pulmonate snails, Physa acuta (Physidae) and Lymnaea columella (Lymnaeidae), were introduced to South Africa probably through the aquarium industry in the 1940s and have now spread to most of the country's freshwater systems. A third invasive pulmonate, and second physid provisionally called Aplexa cf. marmorata, has recently been found in South African freshwaters. Comparison between A.. cf. marmorata found in Durban and P. acuta from Pietermaritzburg as an example of the genus Physa, confirmed that they belong to different genera and are therefore different species. Features compared were the shell, radula, foot, mantle, male genitalia and sperm morphology. Aplexa cf. marmorata is characterized by its foot having a pointed posterior end with a dark mid-dorsal stripe while that of P. acuta does not have these features. The mantle edge ofA.cf. marmorata has short triangular dentations while that of P. acuta has long finger-like projections. Aplexa cf. marmorata does not have an externally visible preputial gland whereas P. acuta does. The penis of A.cf. marmorata has a lateral opening while that of P. acuta has a sub-terminal outlet. TEM sections of the spermatozoon of A.cf. marmorata showed that it has a maximum of two glycogen helices around the mid-piece while P. acuta is known to have three. A study of the population dynamics of A.cf. marmorata in Durban showed it to produce three overlapping generations within a 14 month period whereas P. acuta has been shown to produce as many as eight over a similar time period. Further comparisons between South African A. cf. marmorata and similar material from the West Indies, Nigeria and St Lucia (KwaZulu-Natal) showed that they shared the same features with the specimens collected in Durban and are therefore considered to belong to the same species , Aplexa marmorata (Guilding, 1828). This species is indigenous to the Caribbean and northern parts of South America. The picture is however complicated by the fact that Dr L Paraense, doyen of the Brazilian school of freshwater malacology, does not recognize the genus Aplexa and redescribed this species under the name Physa marmorata in 1986.
Aspects of the biology, specific status and control of the bedbugs Cimex lectularius and Cimex hemipterus in northern Natal and KwaZulu.
(1989) Newberry, Keith.; Appleton, Christopher Charles.
The bedbugs Cimex lectularius and C. hemipterus (Hemiptera: Cimicidae) have been identified from a study area in northern Natal and KwaZulu. South Africa, between 26° 45' S and 28° 45' S, and 32° 00 ' E and 32° 52' E. Morphological behavioural data suggest that the pigeon bug, C. columbarius, which closely resembles C. lectularius, is not present in Zulu huts. Two characters are suggested to supplement Usinger's (1966) key for distinguishing the nymphal stages of C. lectularius, and a key is presented for the case of G. hemipterus. Distinguishing features between the nymphal stages of the two species are also given. The two species were found to be sympatric over most of the study area, with C. hemipterus the more plentiful species in the north and apparently still in the process of invading the study area. Evidence was found that C. hemipterus replaces C. lectularius in huts where initially both species were found, and this agrees with laboratory findings that interspecific mating tends to shorten the life span and reduce the egg production of female C. lectularius females. Interspecifically mated female C. lectularius can be recognised by an easily visible morphological change in the reproductive system (Walpole, 1988b) and this character was used to prove that interspecific mating takes place in the wild. The size and life-stage composition of bedbug infestations were investigated together with factors likely to affect their growth. Cimex hemipterus was found not to be at a disadvantage as regards rate of egg production despite low temperatures in the wild, which suggested that such interspecific differences apparent in the laboratory may be an artifact. The specific status of C. lectularius and C. hemipterus are discussed, with particular reference to their cross-mating in the wild and the production of a hybrid. The acceptability of the Recognition Concept of species (Paterson, 1985) is considered in detail. The susceptibilities of wild bedbugs of both species to DDT, dieldrin and fenitrothion were tested in comparison with a susceptible strain of C. lectularius. Field trials of bendiocarb, deltamethrin and fenitrothion were carried out involving monitoring by bioassay and insecticidal knockdown. Subsequent to successful bedbug control operations, reinfestation rates and rates of replastering of mud walls of huts (an indigenous method of attempted bedbug control inimicable to malaria control operations) are assessed.
The ecology, over-wintering and population dynamics of the pre-imaginal stages of the Anopheles gambiae Giles complex (Diptera : culicidae) in northern Natal, South Africa.
(1991) Le Sueur, David.; Appleton, Christopher Charles.
This study investigated aspects of the breeding biology, ecophysiology, morphology, over-wintering and population dynamics of the pre-imaginal stages of members of the Anopheles gambiae complex in northern Natal, South Africa, Investigation of the breeding biology, concentrated on breeding site utilisation by the different members of the Anopheles gambiae complex. Surveillance personnel were unable to locate the breeding sites of Anopheles arabiensis and postulated that location and description of these would offer a unique opportunity for control. The difficulty in locating the breeding sites of An. arabiensis at certain localities was found to be a product of their low density, presumably as a result of the intra-domiciliary, residual insecticide spray programme. The effect of temperature on larval physiology and adult morphology was investigated. terms of their implications Anopheles gambiae complex. The findings are discussed in for anopheline taxonomy and the The effect of temperature on larval growth rates was investigated in both the field and laboratory. The finding of this part of the study indicate that the larval stages play an important role in the over-wintering of populations within the region. The control implications of these findings and winter breeding site localisation are discussed. A theory for the so called 'late season transmission i.e. Apri-May, within the province and southern Africa is proposed. The population dynamics of An. merus were investigated, together with the effect of abiotic factors such as temperature, salinity and rainfall. The effect of sampling bias due to factors such as behavioural avoidance were studied.
Ecophysiology and population dynamics of the alien invasive gastropod Tarebia granifera in the iSimangaliso Wetland Park, South Africa.
(2012) Miranda, Nelson Augusto Feranandes.; Perissinotto, Renzo.; Appleton, Christopher Charles.
Tarebia granifera is a prosobranch freshwater gastropod from south-east Asia which has invaded other sub-tropical parts of the world. This snail has recently also invaded the iSimangaliso Wetland Park, often reaching population densities of over 20000 ind.mˉ2 and dominating benthic invertebrate communities. A multiple method approach was used to address several aspects of the biology and ecology of this non-native invasive species (NIS). The tolerance of T. granifera to salinity and temperature was investigated through the experimental manipulation of these factors. T. granifera survived exposure to temperatures between 0 ºC and 47.5 ºC. More remarkably, this snail was able to survive a salinity of 30 for 65 - 75 days. Population density and size structure were monitored in estuaries and coastal lakes. T. granifera successfully invaded estuaries despite frequent exposure to high salinity and desiccation. The persistence of T. granifera was largely ensured due to the wider environmental tolerance of adults (20 - 30 mm shell height) which carried an average of 158 ± 12.8 SD brooded juveniles. Multiple introductions were not essential for the success of this parthenogenetic NIS. Using gut fluorescence and carbon budget techniques it was estimated that T. granifera consumes 0.5 - 35% of the total available microphytobenthic biomass per day, or 1.2 - 68% of the daily primary benthic production. The carbon component estimated from the gut fluorescence technique contributed 8.7 - 40.9% of the total gut organic carbon content. A stable isotope mixing model was used together with gut content analysis to estimate the diet of T. granifera and dominant native gastropod species, potentially competing for resources. Results were used in the formulation of an index of isotopic dietary overlap (IDO, %). This approach yielded detailed information both on general changes in ecosystem functioning and specific species interactions. Before/After-Control/Impact (BACI) logic was used in a multivariate approach to separate human perturbations from natural spatio-temporal variability displayed by communities, and to further separate perturbations due to NIS. Human intensification of drought negatively affected biodiversity and T. granifera may exacerbate this problem by displacing native species from critical refugia and contributing towards biotic homogenization. The present findings constitute a contribution to the scientific knowledge on biological invasions and a useful tool towards adaptive management in the iSimangaliso Park.
Effect of soil factors on parasitic nematodes of sugarcane in KwaZulu- Natal, South Africa.
(2004) Dana, Pelisa.; Cadet, P.; Spaull, Vaughan William.; Appleton, Christopher Charles.
Nematicides are not only expensive and unaffordable to small-scale farmers but are also harmful to the environment as they kill both the target organisms and non-target micro and macro-organisms, thereby destabilising the ecosystem. Most developed countries have or are in the process of banning use of chemicals for pest management, implying that agricultural products from developing countries using pesticides will not be marketed in the developed countries. In former studies, it was shown that plant parasitic nematodes posed serious problems in sugarcane fields as their attacks on sett roots during germination period decreased sett root weights, delayed bud germination or led to fewer buds germinating as most buds abort. Those that germinate later are then faced with competition for food, space and light from the "older" shoots and often die. The attacks on shoot roots may lead to inefficient uptake of water and nutrients by the plant thereby leading to stunted plants. Fewer and shorter sugarcane stalks due to nematode attacks result in poor yield. In this study, it has been shown that a large number of endoparasites would be needed to reduce sett root weights. Agricultural systems based on monoculture are rarely successful in the long term and because sugarcane fields have been monocultured for a very long time, they are losing their productive capacity and this is termed "Yield Decline". Instead of using nematicides, alternative methods can be used for the management of nematode communities. Research has shown on other plants that nematode communities dominated by Helicotylenchus dihystera are less pathogenic to the plants than other ectoparasitic nematodes, e.g., Xiphinema elongatum and Paratrichodorus spp. A study conducted as a pot experiment showed that sugarcane grown in soil with high H. dihystera grew taller and produced greater root and aerial biomass than one grown in X elongatum infested soil. To induce a nematode community dominated by H. dihystera in the field, two strategies were followed: (i ) abiotic factors that influence the nematode's environment were identified. Certain elements found in soil and sugarcane leaves were found to be correlated to certain species, e.g., H. dihystera was negatively correlated to soil sulphur, medium and coarse sand while X elongatum was positively correlated to these soil types and soil elements. Sugarcane leaves with high levels of Ca, Zn, Cu and Fe were found in areas with high percentages of H. dihystera while the reverse was true for X elongatum. (ii) organic amendments were used to improve the sugarcane growth, modify the environment and decrease competition among species within a community. Application of organic matter to the soil improves soil properties such as water infiltration, water holding capacity, erodibility and nutrient cycling, increases suppressiveness of soils to plant parasitic nematodes and stimulates other anti-nematode micro-organisms, e.g., nematode-trapping fungi. Organic amendments were therefore used in this study not only as screens to protect sugarcane roots from nematode attacks but also to manipulate nematode communities for the less pathogenic species, H. dihystera. In a field study where organic amendments were used, plots treated with filter cake, thume + filter cake, trash + filter cake, filter cake + furfural and Temik (aldicarb) had high percentages of H. dihystera while control plots had high percentages of X elongatum. However, the change in relative proportion of H. dihystera by certain treatments was not followed by an average increase in yield, probability because of the overall variability. The yield results, however, showed that for all treatments, including control, the highest yields corresponded to plots with higher H. dihystera proportions, conflicting the initial hypothesis. As a result, if an organic amendment that can substantially increase the relative proportions of H. dihystera can be found, a substantial increase in yield can be expected. Although the organic amendments did not successfully manipulate the nematode communities for the less pathogenic species, H. dihystera, plots with higher yield were those that had high H. dihystera percentages in their nematode communities.
Effects of temperature on members of the Anopheles gambiae complex (Diptera: Culicidae) in South Africa : implications for malaria transmission and control.
(1996) Maharaj, Rajendra.; Appleton, Christopher Charles.; Le Sueur, David.
This study investigated the effects of temperature and relative humidity (both controlled and natural) on the lifecyle and morphology of adults of members of the Anopheles gambiae complex in northern KwaZulu-Natal, South Africa. Laboratory investigations into the effects of simulated temperature and relative humidity regimes concentrated on seasonal differences in longevity, egg hatchability, reproductive potential and adult survivorship of An. arabiensis. Differences were found in the life table parameters when these mosquitoes were reared under conditions of seasonal temperature and relative humidity. During the cool season the lifespan and adult survivorship of mosquitoes were greater than those reared during the warm season. In summer, the egg hatchability and reproductive potential were greatest whereas in winter An. arabiensis underwent gonotrophic dissociation although these females were found to take blood meals readily. The influence of seasonal temperature and relative humidity on the body size of An. arabiensis was investigated, both in the laboratory and under field conditions. In both environments, these factors were found to significantly influence body size. In winter, there was a 13% increase in wing size compared to summer bred mosquitoes. A comparison of body size of An. arabiensis, An. merus and An. gambiae reared under laboratory conditions of seasonal temperature and relative humidity showed that the wing size of An. arabiensis was greater than that of An. merus and An. gambiae. The effect of temperature and relative humidity on morphological criteria used in species separation was also investigated. Seasonal differences in wing spot size were compared for An. arabiensis, An. merus and An. gambiae. From this investigation it was concluded that the pale and dark spots on the wing of Anopheles mosquitoes could not be used in species identification due to the large degree of inter-species overlap in the wing spot measurements. The measurement of the pale band at the junction of the 3rd and 4th tarsomere on the hind leg was also investigated for its use in species separation and were found to be useful within the An. gambiae complex. The implications of this study on the transmission and control of malaria are discussed with reference to the late season transmission during March to May that is characteristic of the region.
The invasive potential of the freshwater snail Radix rubiginosa recently introduced into South Africa.
(2011) Nadasan, Devandren Subramoney.; Appleton, Christopher Charles.
Invasions of ecosystems by exotic species are increasing and they may often act as a significant driver of the homogenization of the Earth’s biota, resulting in global biodiversity loss. Moreover, the addition of exotic species may have dramatic effects on ecosystem structure and functioning which may result in the extirpation of indigenous species. In 2004, a large population of an unknown lymnaeid was found in the Amatikulu Hatchery, northern KwaZulu-Natal, South Africa, and was subsequently found in few garden fish ponds in Durban. In 2007, it was identified using molecular techniques as Radix rubiginosa (Michelin, 1831) – a species widespread in southeast Asia. An invasion by R. rubiginosa is however likely to go unnoticed because its shell morphology resembles some forms of the highly variable and widely distributed indigenous lymnaeid, Lymnaea natalensis Krauss, 1848. Accurate and “easy” species identifications would permit the ready assessment of introduction histories and distributions, but in the present case identification was difficult due to unclear and contradicting accounts of the indigenous L. natalensis in the literature. A redescription of L. natalensis with emphasis on conchological and anatomical characteristics was therefore presented. This will help to distinguish variation between R. rubiginosa and L. natalensis and also assist those carrying out rapid bioassessment (SASS) surveys in South African rivers in recognising R. rubiginosa should it spread. For this, shells of R. rubiginosa and L. natalensis from both the UKZN Pond and the Greyville Pond were selected into either size class 1 (shell length < 10 mm) or size class 2 (shell length ≥ 10 mm). Six shell characters, shell length (height), shell width, aperture length (height), aperture width, length of last body whorl and spire height for each specimen was measured and analysed using principal component analysis (PCA) and The invasive potential of the freshwater snail Radix rubiginosa recently introduced into South Africa discriminant functions analysis (DFA). The most useful discriminant conchological characters were shell length, length of the last body whorl and aperture width. Use of these shell characters provided simple yet effective criteria for the separation of R. rubiginosa and L. natalensis. For both size classes R. rubiginosa had larger, more broadly ovate shells with longer (higher) body whorls than either of the two populations of L. natalensis that exhibited smaller, elongated shells with shorter (lower) body whorls. Also, R. rubiginosa had a narrower aperture width compared to the larger, wider aperture of the UKZN Pond L. natalensis population. The Greyville L. natalensis population was found to have narrower apertures than both R. rubiginosa and L. natalensis (UKZN Pond). The morphology of the radula and the reproductive anatomy of R. rubiginosa and L. natalensis from both the UKZN and Greyville Ponds showed little variation. The species did however vary in the relative numbers of radula teeth in each field and this serves as an additional useful diagnostic character. Both L. natalensis populations had similar mantle pigmentation patterns but that of R. rubiginosa was different. The mantle surface of R. rubiginosa was mottled black with patches of pale white to yellow. There were also large unpigmented fields and stripes that were not observed in L. natalensis. Having found characters to conveniently separate the alien R. rubiginosa from the indigenous L. natalensis, it became increasingly important to assess the potential invasiveness of this introduced species and its likely impact. The potential invasiveness of R. rubiginosa was assessed in relation to the already invasive North American Physidae Physa acuta Draparnaud, 1805 and the indigenous L. natalensis. This was particularly important in view of the success of P. acuta as an invader in South Africa. The hatching success, frequency of egg abnormalities, embryonic development, growth, survivorship, fecundity and life history parameters (GRR, Ro, rm, T and λ) for the four snail populations were assessed at three experimental temperatures (20oC, 25oC and 30oC). The invasive potential of the freshwater snail Radix rubiginosa recently introduced into South Africa The results showed that R. rubiginosa and P. acuta had a higher growth coefficient (K), longer survivorship, higher fecundity (higher hatching success, fewer egg abnormalities, longer duration of oviposition), shorter incubation period, greater life history parameters (GRR, Ro, rm and λ) and wider temperature tolerances than the two L. natalensis populations tested. The high adaptability of P. acuta to changing environmental factors such as temperature, is in agreement with the fact that it is now more widespread in South Africa than the indigenous species L. natalensis. This has important implications for R. rubiginosa, since this species displayed reproductive attributes and a temperature tolerance that were similar and in certain cases even exceeded the performance of the invasive P. acuta. This therefore implies that R. rubiginosa has the potential to colonize a wider geographical and altitudinal range than L. natalensis, and perhaps even P. acuta. Also, the superior reproductive ability of R. rubiginosa over L. natalensis is likely to present a situation that allows for its rapid spread as well as a possible impact on the indigenous L. natalensis that might render it vulnerable.
Plant molluscicides for snail control in the South African context.
(1994) Clark, Tanza Elizabeth.; Appleton, Christopher Charles.; Drewes, Siegfried Ernst.
Despite more than half a century of international research on schistosomiasis control, this disease remains a public health concern in many Third World countries. Four to five percent of the world's population is estimated to be infected. In South Africa, bilharzia is prevalent in rural communities which lack piped water and adequate sanitation. Transport and treatment costs limit access to Western medication. In the last decade, plant molluscicides have received considerable attention in the ongoing search for cheaper alternatives to chemotherapy and synthetic molluscicides. Plant molluscicides may be locally harvested, extracted and applied for the control of the snail host. This approach is based on a philosophy of self-reliance and self-determination. However, such involvement presupposes recognition of the infection as a real problem. Before selecting and evaluating plants for molluscicidal activity, it was first necessary to establish the status of schistosomiasis in rural communities, and the willingness of community members to become involved in control efforts. Field surveys showed that rural South African communities do not share the indifference of the past health-care system towards schistosomiasis in this country. Concern for the disease was matched by a prevalence of 75.14% for S. haematobium in the study area. The potential of the South African flora to provide suitable molluscicidal candidates has never been systematically assessed . As random screening is costly and is historically of limited success, a need has existed for the development of an objective selection procedure . A simple scoring system was devised, based on the criteria for "good" plant molluscicides as defined by the World Health Organization (WHO). Three plant species were subsequently selected for further intensive evaluation: Warburgia salutaris, Gardenia thunbergia and Apodytes dimidiata. Initially, the activity of crude aqueous suspensions of all three candidates was investigated, since this application form is the most practical for use in a rural situation. Further, the stability of extracts under changing physical and chemical conditions was assessed, as were t he effects of molluscicides on a wide range of to the toxicity of aqueous suspensions, cultivation potential, medicinal value, stability, and toxicity to non-target organisms. Studies on the mode of action of the three plant extracts revealed that death occurred via distinct physiological pathways; this despite the similarities in clinical symptoms. Such is the complexity of snail physiology that until more intensive neurological investigations are undertaken, the mechanisms of molluscicidal action can only be inferred. Chemical compounds responsible for activity were identified from Apodytes dimidiata; genipin, a monoterpene, was one such active constituent. Although not previously recorded as molluscicidal, earlier workers have isolated genipin from Genipa americana and Gardenia jasminoides. Notably, this compound has not yet been isolated from Gardenia thunbergia. Further activity in A. dimidiata extracts appeared to be the result of a synergistic effect, potentially involving (S)(-) ethyllactate. Research on mammalian toxicity, and registration procedures for plant molluscicides in South Africa should be prioritized for further investigation, before pilot field trials are initiated. Almost thirty years have passed since the first reports on the activity of Phyto!acca dodecandra. Although more than 1000 plant species have since been tested world-wide, it appears that no plant molluscicide has ever been endorsed by the WHO. More concerted efforts are necessary to ensure that appropriate molluscicidal technologies are provided to infected communities.
The role of Anopheles arabiensis (Diptera: Culicidae) in malaria transmission and control in Gokwe and Binga districts, Zimbabwe..
(1996) Masendu, Hieronymo Takundwa.; Sharp, Brian Leslie.; Appleton, Christopher Charles.
Opportunistic feeding behaviour and partial exophily make An. arabiensis much more difficult to control by indoor residual spraying than any other vector in the Afro-tropical region. The persistent malaria outbreaks in Zimbabwe despite decades of indoor house spraying prompted this investigation into the role of An. arabiensis in malaria transmission and assessment of the possible impact of this control measure. The study was conducted in the malaria endemic districts of Binga and Gokwe. An. gambiae complex mosquitoes were collected from artificial outdoor resting sites, and from human dwellings by i) daytime hut searches, ii) pyrethrum spray catches and iii) exit window traps. Mosquito components were processed to enable: i) the distinction of An. arabiensis from An. quadriannulatus and An. merus on the basis of the pale band at the junction of the hind leg 3/4 tarsomeres; ii) species identification and scoring of inversion polymorphism on the basis of the X chromosome and autosomes respectively; iii) the determination of blood meal sources using the Ouchterlony precipitin test; and iv) identification of An. gambiae s.l. using polymerase chain reaction (PCR) and enzyme electrophoresis techniques. Entomological assessment of residual spraying included determining: the vector resting densities indoors and outdoors, bioassay and insecticides susceptibility tests. Data were also collected on hut profiles, knowledge-attitudes-practices surveys, and household malaria prevalence . surveys. An. arabiensis and An. quadriannulatus were found in sympatry in Binga and Gokwe, and in addition, An. merus was found in Gokwe. Most species identifications were made using PCR; which was found to have 7.5% and 41.6% levels of error for An. arabiensis and An. quadriannulatus respectively, using the cytogenetic technique as benchmark. The pale band technique yielded > 80% correct identification for An. arabiensis but the extent of overlap in the pale band lengths between An. arabiensis and An. quadriannulatus renders the method unsuitable for distinguishing these two species. Inversions 2Rb and 3Ra were found floating in An. arabiensis, with 60% frequency in the former. The Wright's F statistic value of -0.0416 indicated an excess of heterozygotes, and a state of panmixis in the vector population. No significant differences were observed between 2Rb karyotypes in host choice. Human blood indices among indoor (0.82), exit trap (0.98) and outdoor resting (0.30) specimens suggested exophilic behaviour. This was corroborated by the high fed:gravid ratios of 6.8: 1 and 11.6: 1 in sprayed and non-sprayed dwellings respectively. This was worsened by a high feeder-survivor index (FSI) of 93 % among exit trap specimens. The susceptibility to deltamethrin coupled with residual efficacy nine weeks post-spray indicated the suitability of the insecticide. Rural dwellings were suitably built for spraying but had no mosquito proofing. Personal protective measures are hardly known; sleeping outdoors occurs in Siabuwa. While An. arabiensis bites humans indoors the partial exophily it exhibits is a threat to indoor residual insecticide spraying. An integrated malaria control approach is recommended.
Studies on the biology of three species of sea urchin (Echinodermata : Echnoidea), on the South African east coast.
(1993) Drummond, Anne E.; Heeg, Jan.; Appleton, Christopher Charles.
Ten species of shallow water echinoid are found on the subtropical east coast of South Africa. Although their distributions are patchy, the most common species, Echinometra mathaei, stomopneustes variolaris and Diadema savignyi, are nontheless conspicuous components of intertidal communities on this coast. As little was known about these three species, the overall intention of this study was to provide some fundemental information on their biology and ecology. For the purposes of achieving this aim a life history approach was adopted, where the relative investments by each species in growth, maintenance and reproduction were investigated and compared. These patterns of investment were then related to the habitat occupied by each species, in an attempt to identify the selective forces which may have been implicated in shaping their life histories. It was apparent from the results of investigations conducted between January 1991 and June 1993 that there were distinct differences in the patterns of investment in growth, maintenance and reproduction between the three species. The life history of S. variolaris, which occupied exposed habitats in the lower intertidal, was characterised by a large investment in maintenance, lower reproductive output, slower growth and a longer lifespan, relative to the other two species. In contrast, Q. savignyi, which inhabited less exposed mid-shore pools, had a relatively higher reproductive output, more rapid growth, a smaller investment in maintenance and a shorter lifespan. While selection ln S. variolaris and Q. savignyi appears to favour survival and reproduction respectively, the life history of E. mathaei, a species which also occupies mid-shore pools, was balanced between these two extremes, allocating sufficient resources to maintenance to permit tolerance of harsh physical conditions while still making a moderate investment in reproduction over a lifespan of intermediate duration. The predictions generated by the r-K selection and "bet hedging" theories of life history evolution, were applied in the process of speculating on the selective forces which may have shaped these life histories. However, it was found that neither set of predictions and associated selective forces could adequately explain the observed life histories. Rather, it seemed that the life histories of the three species represented evolved responses to the direct and indirect effects of exposure to wave action and sand movements which dominate the intertidal environment on the South African east coast. In the exposed lower intertidal, unpredictable recruitment, drag and impact forces associated with wave action, which impose limits to body size and necessitate a large investment in maintenance to ensure survival, select for slow growth, low reproductive output and high longevity. In contrast reproduction and growth of species occupying the more sheltered mid-shore pool habitats would be less effected by the demands of maintenance investment or limits to body size. In addition predictable recruitment in the mid-shore, would obviate the need for long life in order to ensure a contribution to future generations.

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